Meet one-on-one with the employee and candidly ask if they are dissatisfied. When faced with a direct question, many people will respond in truth. If the employee says yes, ask why, listen attentively and explore possible remedies that would work for both parties.
If you sense an employee is looking to leave because they want more challenging work, consider offering new responsibilities that will stretch their skills. Provide virtual training opportunities to support their ongoing professional growth. Another idea: Set up a mentoring arrangement. Through mentoring, the employee can gain additional skills and knowledge — and find new enthusiasm for their work and career.